Dynamic range (DR) relates to a span of intensity (e.g., luminance, luma) in an image. The DR in real-world scenes is usually large. Different image and video applications for the capture, representation, and presentation of image and video signals may have different DR. For example, photographic negatives can have a relatively large dynamic range, while photographic prints, some currently existing (e.g., conventional) television (TV) sets, and computer monitors may have a smaller DR.
DR also relates to a capability of the human psychovisual system (HVS) to perceive a range of intensity (e.g., luminance, luma) in an image, e.g., from darkest darks to brightest brights. In this sense, DR relates to a “scene-referred” intensity. DR may also relate to the ability of a display device to adequately or approximately render an intensity range of a particular breadth. In this sense, DR relates to a “display-referred” intensity. In another sense, DR may also refer to a “signal-referred” intensity—which may be to some extent theoretical. For example, a VDR signal may range up to 10,000 nits and HDR signals may range even higher. Most of the time, there are no grading displays for that range. Unless a particular sense is explicitly specified to have particular significance at any point in the description herein, it should be inferred that the term may be used in either sense, e.g. interchangeably.
Rendering by conventional TV sets and computer monitors is often constrained to approximately three orders of magnitude of dynamic range—typifying a low dynamic range (LDR), also referred to as a standard dynamic range (SDR). In contrast to LDR images, high dynamic range (HDR) images contain essentially all of the dynamic range in an original scene. HDR can span some 14-15 orders of magnitude of dynamic range. HDR images can be represented by any bit depth, but typically 10-16 bits or more are used to reduce overly large step sizes.
For a number of applications such as compression for distribution, encoding for HDR images may unnecessary and may in fact be somewhat computationally expensive or bandwidth consumptive. On the other hand, LDR images may simply not suffice either. Instead, such applications may advantageously use, create, store, transmit or render images that may be characterized by a visual dynamic range or variable dynamic range, VDR. VDR images, truncated in relation to HDR, encompass essentially all of the luminance and color that a typical HVS can simultaneously perceive (e.g., visually perceive at any given time). VDR spans about 5-6 orders of magnitude of dynamic range. Thus while narrower in relation to HDR, VDR nonetheless represents a wide DR breadth. Despite the DR differences between HDR and VDR images, the term EDR, as used herein, characterizes any image with an extended dynamic range compared to LDR.